High resolution experimental studies and numerical analysis of fine bubble ozone disinfection contactors

Countercurrent flow hydrodynamics and mass transfer were explored using computational fluid dynamics (CFD) analyses, tracer studies and a novel mass transfer visualization technique. In concert, these techniques yielded a comprehensive description of countercurrent hydrodynamics and mass transfer.; In the laboratory bubble column reactor in which experimental studies were performed, liquid flowed upward with gas bubbles in the core of the bubble plume and downward outside the bubble plume near the cylinder walls at all gas flow rates. CFD predicted a large recirculating flow near the sparger. Well-mixed conditions were observed in a zone termed the entrance length, located near the sparger. Mass transfer visualization experiments allowed estimation of the entrance region length. The entrance region increased as a function of gas flow rate and ranged from a value of about 22% (for the lowest gas to liquid flow ratio experiment) to nearly 40% (for the highest gas to liquid flow ratio experiment).; To demonstrate its utility as a design tool or for troubleshooting underperforming full scale reactors, CFD was used to predict hydrodynamics, Cryptosporidium parvum inactivation and bromate formation in a full scale reactor. Despite being relatively crude the CFD model identified flowfield features conducive to bromate formation or deleterious to C. parvum inactivation. Specifically, in chambers in which ozone is applied, large recirculating flows were predicted. Water detained in these recirculating flows have relatively long detention times and contribute to bromate formation in waters with sufficient bromide content.; The current study demonstrates that, even in a simple tall right circular cylindrical bubble column, hydrodynamics plays a major role in contact of ozone with microorganisms and substances that form bromate. Both experimental and analytical studies identified significant spatial variations in mixing and mass transfer in the relatively simple bubble column reactor. These findings indicate that CFD could be more widely used as a component of pilot scale studies of ozone bubble contactor reactors or in design of full scale contactors. Given current computer prices and speeds, CFD analysis is appropriate for plants with capacities which are smaller than the very large capacity plants for which CFD is presently used.